Summary
For economic and technical reasons, the industry has used directional,
extended-reach, horizontal, and multilateral wells. Although technologies are
well developed for these wells, and there are numerous successes in the last
decade, these wells still have high level of risk in drilling and completion.
Well control is one of the relatively unanswered, but important, operations
because improper well control followed by a blowout is one of the most
expensive and feared operational hazards.
To maintain a specified bottomhole pressure (BHP), surface choke pressures
highly depend on kick vertical height in the well and well trajectory. As the
final hold angle of the well increases from vertical, shut-in casing pressure
(SICP) reduces to shut-in drillpipe pressure (SIDPP) and remains the same as
long as the kick stays in the horizontal section. For equal vertical depths,
the maximum choke pressure is insensitive to hold angles or hold lengths, as
long as the initial pit-volume gain is the same. However, for directional and
extended-reach wells, choke pressure can increase, even without kick expansion,
because of the gain of kick vertical height in the build section. This may mask
choke-pressure reduction because of larger annular capacity when the kick
passes the casing shoe, especially if the kickoff point (KOP) and casing-shoe
depth are close.
In multilateral wells with more than one kicking wellbore, SIDPP is affected
by both formation overpressure and kick size in each wellbore. The maximum
value among them will appear at the surface. Therefore, we should be careful in
the interpretation of the shut-in pressures. For safe kick circulation, we must
consider additional pressure to compensate for hydrostatic-pressure reduction
resulting from kick migration and expansion in branch wellbores.
Introduction
For economic and technical reasons, the industry has used directional,
extended-reach, and horizontal wells. Directional drilling is used to direct a
wellbore along a preplanned path to a target located at a given distance from
the vertical. We can calculate its trajectory accurately if directional data
such as measured depth, inclination angle, and azimuth are known.1 For the
planning of the well trajectory in a two-dimensional plane, we can use
generalized equations,2,3 which are applicable for directional and horizontal
wells, rather than using composite buildup charts or several directional
equations, depending on each trajectory type.
Several wells drilled from one platform for offshore development will reduce
the development cost significantly and make the installation of production
equipment efficient. These wells are also applicable for areas that will not
permit vertical wells because of inaccessible obstructions, limited spaces, or
environmental concerns. Multiple targets can be reached by a single directional
trajectory.
From the production point of view, horizontal or near-horizontal wells are
used to enhance recovery efficiency by increasing reservoir exposure or by
intersecting fractured reservoirs. It can also reduce chances of water coning,
especially for a thin reservoir. They have been used extensively in heavy-oil
reservoirs. In the early 1990s, the industry employed multilateral wells from
which multiple wellbores are drilled from one main wellbore (also called the
“parent” wellbore). Multilateral wells have the same aforementioned advantages.
However, implementation will be much more complex than that of directional
wells with a single wellbore.
Although technologies are well developed for these wells, and there are
numerous successes in the last decade,4,5 these wells still have a high level
of risk concerning drilling, completion, pressure imbalance, communication
among laterals, and production management. It will require multidisplinary
teamwork, thorough planning, and implementation as planned. Because well
control is one of the relatively unanswered but important operations, we must
develop a firm well-control plan for practical applications of these wells.
A kick is defined as an unscheduled flow of formation fluids into a
wellbore. Well control includes several activities for kick prevention, kick
detection, kick confinement, and kick removal with safe and efficient
procedures. The best way of controlling kicks is kick prevention, which may be
achieved through sound and thorough planning and execution.
© 2005. Society of Petroleum Engineers
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History
- Original manuscript received:
11 August 2004
- Revised manuscript received:
30 March 2005
- Manuscript approved:
20 April 2005
- Version of record:
15 June 2005
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